Musical instruments may have vibratory elements that vibrate at audio frequencies. The frequency of vibration of these vibratory elements is precisely adjusted to control the pitch of the musical instrument, a process hereinafter referred to as tuning. Commonly an electronic device is used to measure these frequencies and display appropriate information to the operator to facilitate the tuning process. This electronic device requires the audio frequency vibrations from the musical instrument to be converted to an electrical signal that is compatible with the device. Several methods have been used to achieve this including microphones, direct electrical connection to a musical instrument with built-in transducers and direct contact sensors such as piezo-electric materials or accelerometers. All of these methods have inherent limitations and undesirable characteristics which affect the ability to tune the musical instrument.
Microphones are sensitive to sound in the surroundings, which often makes it difficult or impossible to tune the musical instrument. Direct electrical connection is only possible for those musical instruments that include built-in transducers. Even when a direct electrical connection is present it can be inconvenient to use because the connection between the musical instrument and its sound-generating device must be broken to connect the electronic tuning device and then re-established after tuning is complete. Direct contact sensors must be in intimate physical contact with the musical instrument to sense its vibrations and often the reliability of the tuning process critically depends on the exact positioning of the sensors on the musical instrument. Moreover, such sensors often do not respond well to low frequencies and the intimate physical contact required can be undesirable when used with valuable musical instruments.
By using stroboscope techniques, where the vibratory element will appear motionless when the frequency of the strobe light corresponds with the frequency of vibration of the vibratory element, it is possible to circumvent the aforementioned inherent limitations. However this method requires an experienced operator and it does not work well on vibratory elements whose motion is difficult to observe by the human eye. Moreover, low-frequency strobe lights can cause discomfort for the operator.
Optical pick-ups for musical instruments have been described that must be mounted onto a musical instrument. U.S. Pat. No. 5,214,232 describes a musical instrument equipped with a detector optically detecting string vibrations. U.S. Pat. No. 4,815,353 describes a photoelectric transducer that is mounted onto a musical instrument. Neither document describes tuning the musical instrument.
Both of these documents require that the relative positioning of the detecting elements and the vibratory elements to be carefully controlled via predetermined geometry of the rigid body of the musical instrument. This requirement ensures the vibratory element remains within (what is described in U.S. Pat. No. 5,214,232 as) the linear zone, and that the magnitude of the measured signal is substantially proportional to the photo current in the detecting element. In addition, the electronic circuits of these documents require precise adjustment for each vibratory element being measured. Such inherent limitations preclude the use of these in a situation where the relative position of the photo emitting and photo detecting elements and the vibratory elements cannot be controlled, and where a variety of vibratory elements may be encountered.
Therefore a need exists for a device that can convert the frequency of vibrations of a vibratory element of a musical instrument to an electrical signal so that it can be sent to an electronic tuning device so that the musical instrument can be tuned without making physical or electrical contact with the vibratory element, or with the musical instrument which comprises said vibratory element, and which is insensitive to sound in the surroundings.